Of course, the phrasing _If gender dysphoria is caused by ..._ implies that we're considering _gender dysphoria_ as one category to reason about homogeneously. But different people might want to transition for very different underlying psychological reasons. What categories we use may not be a question of simple fact that we can get wrong, but if, empirically, there happens to be a sufficiently robust statistical structure to the simple facts of the cases—if some people want to transition for reason _A_ and tend to have traits _W_ and _X_, but others want to transition for reason _B_ and have traits _Y_ and _Z_—then aspiring epistemic rationalists may find it useful to distinguish multiple, distinct psychological conditions that all happen to cause gender dysphoria as a symptom.
Analogously, in medicine, many different pathogens can cause the same symptoms (_e.g._, sneezing, or fever), but doctors care about distinguishing different illnesses by etiology, not just symptoms, because distinct physical mechanisms can give rise to distinct treatment decisions, if not immediately, then at least in principle. (For example, a bacterial illness will respond to antibiotics, but a viral one won't—or today's treatments might be equally effective against two different species of bacteria, but future drugs might work better on one or the other.)
Of course, the phrasing _If gender dysphoria is caused by ..._ implies that we're considering _gender dysphoria_ as one category to reason about homogeneously. But different people might want to transition for very different underlying psychological reasons. What categories we use may not be a question of simple fact that we can get wrong, but if, empirically, there happens to be a sufficiently robust statistical structure to the simple facts of the cases—if some people want to transition for reason _A_ and tend to have traits _W_ and _X_, but others want to transition for reason _B_ and have traits _Y_ and _Z_—then aspiring epistemic rationalists may find it useful to distinguish multiple, distinct psychological conditions that all happen to cause gender dysphoria as a symptom.
Analogously, in medicine, many different pathogens can cause the same symptoms (_e.g._, sneezing, or fever), but doctors care about distinguishing different illnesses by etiology, not just symptoms, because distinct physical mechanisms can give rise to distinct treatment decisions, if not immediately, then at least in principle. (For example, a bacterial illness will respond to antibiotics, but a viral one won't—or today's treatments might be equally effective against two different species of bacteria, but future drugs might work better on one or the other.)